Can We Prevent EHD?

Hemorrhagic disease (HD) hit whitetails extremely hard in 2012, the latest in a recent string of notable years for outbreaks. The disease (mostly strains of a virus known as epizootic hemorrhagic disease or EHD, but which also includes the closely related bluetongue virus) is striking areas that were previously unaffected, or rarely affected. In these areas it is having its worst impact, because whitetails have less history with the disease and therefore less acquired resistance to the viruses.

Wherever the virus strikes, the losses have hunters asking: What can we do to prevent EHD? I talked to an expert about a factor that is probably more well known than any other: the insect that spreads the virus. What I learned could help deer hunters reduce the risk or severity of EHD and bluetongue outbreaks.

Meet the Midge
EHD and bluetongue are spread in cattle, deer and other ruminants by several species of a tiny flying insect in the genus Culicoides. Call it a gnat, a midge, a no-see-um, or any other local name, this is the tiny fly with the big bite. Three species are the primary vectors, or transmitters, of HD viruses, but one of them is considered the most significant vector and the one we know the most about: Culicoides sonorensis.

Now retired, Ed Schmidtmann spent most of his career as a researcher with the Arthropod-Borne Animal Diseases Research Unit, part of the USDA Agricultural Research Service. Ed studied insects and ticks that transmit diseases, and sonorensis was one of his special interests. If there is a way to reduce midge numbers and thus reduce the spread of HD, it relates to their breeding habitat: the shallow margins of ponds.

The worm-like larvae of all Culicoides species are tiny – about 2 to 4mm long (the height of a capital letter in the text you are reading right now). After hatching from eggs, the larvae live in submerged mud at the very edge of shallow standing waters. They are found in water less than 2 inches deep. The ideal water is warm, sunlit, high in organic matter, high in nutrients and low in oxygen (“eutrophic” is the scientific term for this low-quality water). Disturbed mud is also ideal. Thus, perfect conditions for midge reproduction are created in the typical cattle pond, where cattle disturb and disrupt the shallow margin of the water and prevent plant growth while also defecating and urinating in the water, increasing eutrophication.

“If I wanted to find the larvae of this insect, I’d look in a cattle pond,” said Ed. “Captive deer create the same kind of situation, it isn’t just cattle.”

Because larvae live in sediments at the water’s edge, and are not open-water creatures like mosquito larvae, they have few aquatic predators.

“One thing that makes this insect very adaptable is its tolerance of salts,” said Ed, “and that seems to be a key feature of the habitat because it allows the insect to live in a pure culture without other insect competitors.”

Salt levels are often high in cattle ponds due to salts fed to the cattle or leached into the standing water from feedlot runoff. These salts kill off other insect populations, reducing the midge’s competitors and giving the midge abundant breeding space.

Once larvae mature, they leave the water and morph into winged adults. Only the females feed on blood. The females are crepuscular – most active at dawn and dusk – just like deer.

“They’re not very strong fliers, so calm, humid nights are ideal for feeding,” said Ed.

Females convert the protein in their blood meals into egg production. When they feed on deer, the viruses they are carrying can be transmitted to deer, or from the deer to the midge. Females lay their eggs in the soil at the edge of a suitable body of water, the eggs hatch into larvae, and the cycle continues.

Add Drought and Summer Heat
Why do outbreaks of HD tend to be worse in abnormally hot, dry summers? As water holes dry up during drought, organic material, other contaminants and salts become even more concentrated in the remaining water, which is also likely warmer and shallower. Thus, conditions for midge reproduction are further enhanced.

Heat and drought also increase water consumption in cattle and deer (and feral hogs if you have those), so they are drawn more often to a dwindling supply of water holes to quench their thirst and cool off, increasing edge disturbance and the amount of animal waste and urine excreted directly into the water – again enhancing midge breeding conditions. Deer are usually able to get most of the water they need from succulent forage, but forage quantity and moisture content shrinks during summer droughts. As thirsty deer concentrate around limited water sources, where midge reproduction is in high output, contact between feeding midges and deer is even more frequent.

Extended periods of peak summer heat also mean extended breeding seasons for the midge. Female midges are not limited to one egg-laying cycle and can continue producing and laying eggs (in cycles every three to five days, according to Ed) until they die or are killed by the onset of cold weather. Meanwhile their offspring from earlier egg-laying cycles are joining the adult population. Thus, midge abundance builds exponentially as warm weather endures in late summer.

Wait, there’s more. According to Ed, warm weather also increases the rate of virus growth inside the body of an infected female midge. As warm weather is prolonged, and the female midge enjoys a longer lifespan than they would in cooler summers, the virus count builds, increasing the likelihood the virus will be transmitted each time the midge bites a deer.

Many deer managers have constructed small water holes for deer as part of an effort to create complete wildlife habitat that helps attract and hold deer. If you are one of them, you may be thinking about that water hole right now and wondering: Is it actually a danger to deer?

What You Can Do
If you’ve already constructed a deer watering hole and it sounds like the ideal midge breeding grounds I’ve described here – shallow, murky, warm, exposed to direct sunlight, with a muddy or silty bank that is regularly disturbed in summer by cattle, deer or feral hogs – consider ways you may be able to alter the water source, or the ways animals use it, to avoid enhancing midge reproduction.

Alternatively, when creating new water sources for deer, plan appropriately.

According to Ed, midge reproduction is minimal in clean, clear, deep bodies of water, or where banks are vegetated or rocky (rather than muddy) or where the bank is steep. If you create water holes, try to construct them to produce healthy, vegetated wetlands rather than shallow mud holes, or shape them in a way that reduces midge breeding habitat during dry conditions. Locate them in shade to keep water temperatures cooler in summer.

“Create a stable ecology in this wetland habitat,” said Ed. “Encourage vegetation to grow, and design steeper margins for the pond.”

If you provide salt or mineral supplements for deer, do not place them in a location that allows them to leach into nearby standing water.

Unfortunately, many of the factors in play will be out of your control. If cattle operations and ponds are abundant nearby, and you don’t have control over management of the ponds or the cattle, you may be fighting an uphill battle. If you own the cattle, try to find an alternative water supply and fence them out of small farm ponds during summer.

Streams are another factor that may be out of your control. During dry spells, small streams may recede into strings of shallow pools that offer breeding grounds for midges.

Nevertheless, Ed said that taking steps to improve the quality and health of small bodies of water on your hunting land may help.

“Even if you’re only managing 100 acres, if you decrease the availability of breeding habitat through management, it might have an effect on virus transmission,” said Ed.

“If it was a gamble, I’d take it,” said Dave. “It’s like everything else with managing deer: If your neighbors aren’t doing the same things, you may have limited success. But there’s no sense in making trouble for yourself by offering the kinds of places these insects use to reproduce.”

Study the quality of standing water sources where you hunt. It may be that maintaining healthy, abundant deer populations despite HD requires us to offer not just any hole that holds water, but healthy wetlands that are good for more wildlife than just thirsty deer.

Did You Know? QDMA and its volunteer Branches have focused educational efforts in EHD and CWD (chronic wasting disease) outbreak areas, QDMA has advocated for wise disease-management policy at the state and federal level, and QDMA has directed funding toward research into diseases that threaten deer herds. Support QDMA in these and many other efforts to protect deer hunting by joining today!

Gallery

It can be spread to many other wild ruminants. It is not zoonotic (can not be spread to humans). Whitetail deer is the most susceptible.

Posted by veterinaryhog on 2013-04-09 18:54:09

No that is just shedding of their winter coat. There is a good chance EHD is why your does died, but the shedding of their hair is a not a clinical sign of the disease. Deer will go to water because of the extreme temperatures due to the disease, they will often be open mouth breathing and excessive salivation. The deer use rot very quickly due to increased temperatures. Also, I have heard several people say that scavengers will not eat the deer. It is like they know something bad killed the deer.

Posted by veterinaryhog on 2013-04-09 18:51:55

Nice write up, LT!

Posted by Will G. on 2013-04-07 08:05:20

What about the deer in the center photo at the end of the article? The one in the foreground on the left has discolored skin on its neck and back. Is that what EHD looks like before the animal dies? If so, two of my does appeared exactly like that last summer on my property outside Tulsa.

Posted by Tulsa Reiner on 2013-04-05 06:15:49

Hunting in Nebraska National Forest in Halsey, there were many muleys and whitetails that were found at the windmills dead. Horrible hunting. Our whole group walked out without deer and to be honest, we weren't sure if we should have shot anything anyway with the herds hurt already.

Posted by TJ on 2013-04-04 12:25:37

What other animals can acquire EHD?

Posted by BBD117 on 2013-04-03 19:32:35

Here in Michigan we had about 15,000 reported dead deer from EHD last year.I found the first dead deer on July 23rd in our pond. In September our Qdm branch held a meeting at the local high school with the DNR biologist here in southern Mi. We had about 250 people show up.Our township lost about 50% of the deer herd.While shed hunting this year we have found over 150 dead deer.About 90% looked to have been taken from EHD,the other were probably lost by hunters.It's sad to think that for every deer that is reported to the DNR,how many are not or not even found.

Posted by Tom Stafford on 2013-04-03 19:22:18

David, Georgia definitely had sporadic cased of EHD this year, so I'd say that's a strong likelihood. Make sure you also examine the skulls for evidence of a brain abscess, because that is also a possibility for some of the deaths, especially in west central Georgia. We just posted an article with more information about brain abscesses: http://www.qdma.com/articles/d...Thanks for reading and good to hear from you, David!

Posted by Lindsay Thomas Jr. on 2013-04-02 16:10:28

I didn't read a lot about EHD here in GA last year but we have found about 8-10 bucks here in W central Ga while she'd hunting this spring and our neighbor has found about the same. Don't know if it was EHD, coyotes or something else.

David Helmly

Posted by Trailwatcher on 2013-04-02 14:59:56

You are right. There is some “good” news in an outbreak. We know that individual deer that survive will acquire immunity to that virus in the future, and that does that acquire immunity can pass temporary antibodies to their fawns. Also, there may be individual deer that are genetically more resistant, and so the herd gains resistance over time as those without resistance die off. But these are slow processes, and these facts don’t do much to cheer a hunter who has found dozens or hundreds of dead deer where they hunt. If we can take steps to control midge populations, we should. Also, hunters who haven’t experienced a serious outbreak yet may avoid that day even longer if they can avoid helping the insect populations. Thanks for reading and commenting!

Posted by Lindsay Thomas Jr. on 2013-03-25 16:04:47

One element that was left out is the possible positive for a deer herd being subjected to a biting midge. By trying to control the amount of deer that are in contact with biting insects that are positive for passing on ehd you reduce the amount of deer in a given herd that can become immune and pass on better genetics to more fawns. It has been proven that deer can pass on these genetics to fawns. I say let mother nature choose, however I do not believe there is a right or wrong, but this is for sure worth mentioning and if I overlooked it I apologize in advance.

Posted by huntingorfishing on 2013-03-25 15:30:23

Ouch. That is tough. Unfortunately, we heard a lot of stories like yours last year.

Posted by Lindsay Thomas Jr. on 2013-03-25 11:00:02

Stock tanks is a good idea! That's a good way to supply water in a drought without creating breeding habitat for the insects. Thanks for reading!

Posted by Lindsay Thomas Jr. on 2013-03-25 10:58:53

It was so dry here in North Central Kansas that most of the ponds and creeks dried up. I put a couple of 900 gallon stock tanks out and replenished them weekly. Don't know if it made a difference or not, but I only found one dead deer down by the creek in August.

Posted by elkhuntergary on 2013-03-23 15:36:24

A buddy of mine has found about 12 so far here in Pulaski County.

Posted by Lee Highsmith on 2013-03-23 11:56:49

Im in Mo too and weve found about 3 this year

Posted by Brendan Ackerman on 2013-03-23 11:43:13

Missouri, The state was hit pretty hard but,what suprised me was this season deer harvest was near 300,000 and doe harvest up 6 percent.

Posted by Russ Reinagel on 2013-03-21 19:07:42

Last year in Wisconsin we found 100+ deer in a 1000 acre square. A couple bucks over 170".

Posted by Pedersen Outdoors on 2013-03-21 10:30:12

Sorry to hear that, Russ. What state are you located in?

Posted by Lindsay Thomas Jr. on 2013-03-20 21:27:03

Great info. Have 260 ac. with a stream running the length of the property, only water source on farm. We found 8 deer dead along the stream.